The present invention relates to a recording liquid, particularly an yellow recording liquid, employing a pigment which is suitably used for, for example, an ink jet recording device and writing tools such as a ball point pen and marking pen.
Research has been active on various types of ink jet recording methods because they generate less noise and allow fast recording without requiring special fixing on ordinary sheets of paper. A recording liquid to be used in ink jet recording methods needs to possess various properties, which include: a viscosity and surface tension, etc., with the property values in appropriate ranges, the property which does not cause clogging of a fine orifice, the property capable of producing recorded images in clear color tones and with sufficient thickness, and the property which does not undergo any change during preservation or which does not incur deposition or precipitation of a solid component.
In addition to these properties, the recording liquid is further required to have a property which allows recording without limiting the type of recording medium used, as represented by paper, and the property of fast fixing rate with respect to the recording medium, and also superior properties in water resistance, solvent resistance, light resistance, and abrasion resistance, and further the property capable of producing images with superior resolution.
The recording liquid to be used in ink jet recording is generally made up of a pigment as a recording material and a solvent for dissolving the pigment (alternatively, dispersion medium for dispersing the pigment), and the various properties of the recording liquid as exemplified above are heavily influenced by the intrinsic property of the pigment. Thus, it is fairly important to select the pigment appropriately to enable the recording liquid to possess the above properties.
The solubility of the recording material with respect to the solvent (alternatively, dispersibility of the recording material with respect to the dispersion medium) is particularly important, and the solubility (or dispersibility) of the recording material with respect to water and also to a lubricant, which is generally made up of an organic solvent, is least required to maintain a desirable anti-clogging property and dissolution stability (dispersion stability) of the recording material. To this end, for example, (Japanese Unexamined Patent Publication No. 145545/1994 (Tokukaihei 6-145545) (published date May 24, 1994)) discloses an azo dye which is sulfonated (rendered hydrophilic) by dissolving the corresponding azo pigment molecules in an sulfuric acid. The azo dye is dissolved in a liquid such as water to be a water soluble dye and is used as a black ink or reddish brown ink.
However, the recording liquid employing a conventional yellow pigment (yellow recording liquid) as a recording material in reality does not totally satisfy the various properties as listed above due to the fact that the yellow pigment itself is hydrophobic.
Further, a conventional producing method of a recording liquid, in which pigment molecules are dissolved in a solvent after they are treated with an acid and rendered hydrophilic has the problem that the amount of chemicals used in a hydrophilicity rendering process is enormous and it does not permit a continuous process because the method employs a batch system. Further, in some cases, a change in color of the pigment itself is incurred.
The present invention was made to solve the foregoing problems and accordingly it is an object of the present invention to provide an yellow recording liquid having a superior property in spray stability (properties which have an effect on spraying of a recording liquid, such as spray response, stability in forming a liquid droplet, recording ability for a continuous and extended period of time, and spray stability after a long pause in recording, etc.), preservation stability, and water resistance of a recorded image, etc., and also to provide a producing method of such an yellow recording liquid, as well as a method of using it. Another object of the present invention is to provide a yellow recording liquid having a superior property in fixability (no spreading) on a recording medium, light resistance, and weather resistance, etc., and a producing method of such a yellow recording liquid, as well as a method of using it.
In order to solve the foregoing problems, an yellow recording liquid in accordance with the present invention contains yellow pigment particles which are dispersed in a liquid, and the yellow pigment particles are rendered hydrophilic at least on the surface.
With this arrangement, the yellow pigment particles which are rendered hydrophilic on the surface, for example, by sulfonation (xe2x80x9chydrophilic particlesxe2x80x9d hereinafter) blend well with the liquid, and the particles are uniformly dispersed without sitting on a liquid surface and do not aggregate each other. Further, the hydrophilic particles are also hydrophobic by the intrinsic property of the yellow pigment and thus exhibit desirable fixability with respect to the surface of a recording medium (recording surface), regardless of whether the recording surface is hydrophilic or hydrophobic. That is, the recording liquid of the present invention can maintain the uniformly dispersed state of hydrophilic particles as a recording material for an extended period of time, thus realizing an yellow recording liquid having a superior spray stability and preservation stability, as well as desirable water resistance of a recorded image.
In order to solve the foregoing problems, according to the method of using the yellow recording liquid in accordance with the present invention, the yellow pigment particles are used as a recording liquid of an ink jet recording device or as a recording liquid of a writing tool.
With this method, a high quality image with superior time stability, water resistance, and light resistance, and having a clear color tone and sufficient thickness can be produced on the recording medium, regardless of whether the surface of the recording medium is hydrophilic or hydrophobic. Further, because the yellow recording liquid has a superior spray stability and superior preservation stability, when used as a recording liquid of an ink jet recording device, clogging of the nozzle of the recording device can be prevented.
In order to solve the foregoing problems, a producing method of an yellow recording liquid in accordance with the present invention includes the steps of: preparing a solution in which an yellow pigment is dissolved in an acidic liquid; turning the solution into particles; bringing the particles into contact with vapor containing water vapor and creating a supersaturated atmosphere of the vapor; depositing yellow pigment particles which are rendered hydrophilic at least on their surface by allowing water to condense on the surface of the particles; and dispersing the yellow pigment particles deposited in a liquid.
With this method, it is not required to have a step of stirring using a stirrer such as a stirring vane for the purpose of rendering the yellow pigment hydrophilic, and the hydrophilic particles (yellow pigment particles which are rendered hydrophilic at least on the surface) do not come to have a charge by friction, etc., and do not aggregate each other. Thus, the deposited hydrophilic particles can easily be dispersed in the liquid without aggregation, thereby realizing a homogeneous yellow recording liquid in which hydrophilic particles having a uniform particle size are uniformly dispersed.
Further, because the device which generates vapor containing water vapor is used, the process can be carried out conveniently over a short period of time using a simple device. Also, because the hydrophilic particles are formed by deposition, the particle size of the product hydrophilic particles is not influenced by the particle size of the hydrophobic substance used (yellow pigment), and it is also possible to make the particle size of the hydrophilic particles relatively small and uniform, thereby conveniently realizing an yellow recording liquid in which hydrophilic particles having a desired particle size are uniformly dispersed.
For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.